1. Field of the Invention
The present invention generally relates to a method of fabricating a metal-insulator-metal (MIM) capacitor, where a hardmask is formed over the capacitor and a photoresist is patterned above the hardmask, which allows the capacitor and corresponding wiring layer to be simultaneously etched through the photoresist, without damaging the upper plate of the capacitor.
2. Description of the Related Art
Capacitors are widely used in integrated circuit technology. One type of well-known capacitor is the metal-insulator-metal capacitor (MIMCap). This type of capacitor has a lower conductive plate and an upper conductive plate separated by a dielectric. When manufacturing metal-insulator-metal capacitors, the dielectric and the upper plate are patterned on a conductive layer. A photoresist is then formed over the dielectric and upper plate in order to pattern the conductive layer into the lower conductive plate. However, the photoresist can sometimes be too thin at the corners of the upper plate, which causes the corners of the upper plate to be undesirably eroded (rounded) during the patterning of the underlying conductive layer.
In order to overcome this problem, a thicker photoresist could be used. However, as the photoresist becomes thicker, the spacing between structures (capacitors, adjacent wiring, etc.) that can be patterned by the thicker photoresist increases, which undesirably increases the pitch of the wiring. When there is an increase in the pitch of the lines (caused by the wider lines and spaces that result from the thicker resist), there is a decrease in wiring density of that level. This necessitates additional levels to compensate for loss in wirability, and makes the technology less attractive and more expensive.
Alternatively, this problem can be overcome by moving all MIMCaps to a level within the integrated circuit structure that already has a wider pitch. However, this is also unattractive because it necessitates that there be a wider pitch level for designs which have MIMCaps, which again adds cost and complexity.
The invention described below solves this problem without increasing the thickness of the photoresist, and in fact allows an even thinner photoresist to be utilized. Therefore, the invention overcomes the problem of upper plate corner rounding without increasing the pitch of the wiring.